This invention relates to a touch system coordinates input apparatus for calculating the coordinates of an arbitrary point on an input surface pushed by a finger, a pen or the like, by applying the component forces of the push force occurring at a plurality of support points of the panel to a computer or the like.
First, the principles of coordinate detection will be described.
A rigid plate 1 is supported at n points (x.sub.1, y.sub.1), (x.sub.2, y.sub.2), . . . , (x.sub.n, y.sub.n) as shown in FIG. 1. When an arbitrary point (x,y) of this rigid body is pushed with a force in the direction perpendicular to the drawing, component forces f.sub.1, f.sub.2, . . . , f.sub.n, are observed at the support points 2.
From the equilibrium of the forces in the perpendicular direction to the drawing, the following equation can be obtained: EQU F=f.sub.1 +f.sub.2 +. . . +f.sub.n ( 1)
The following formula can be obtained from the equilibrium of the moments around the y axis: EQU x.multidot.F=x.sub.1 .multidot.f.sub.1 +x.sub.2 .multidot.f.sub.2 +. . . +x.sub.n .multidot.f.sub.n (2)
Similarly, the following formula can be obtained from the equilibrium of the moments around the x axis: EQU y.multidot.F=y.sub.1 .multidot.f.sub.1 +y.sub.2 .multidot.f.sub.2 +. . . +y.sub.n .multidot.f.sub.n (3)
From the formulas (1) through (3), the coordinates (x, y) of the push point can be determined as follows: ##EQU1##
FIG. 2 shows an example of the prior art based on the principle described above.
The component forces f.sub.1 -f.sub.3 can be determined by measuring the strain developing at a straining portion 3 by use of a strain guage 4. In this example, the input surface panel has a different structure from the structure of the straining portion 3 (cantilever or the like).
To clarify the point of application of the push force, the straining portion 3 is equipped with a frame 10 and needles 11 as illustrated in FIG. 3.
In accordance with the conventional structure, the point of application of the push force can be clarified but the support structure of the panel 1 becomes complicated, increasing the cost of production of the apparatus as a whole. Furthermore, since the panel 1 is supported by the needles 11, another problem develops in that the mechanical strength of the apparatus in low. Since the frame 10 projects from the panel 1, severe restrictions are imposed on the apparatus design and sometimes cause problems during the operation of the apparatus.